This study analysed the effect of sound sequence on soundscape emotions with respect to three aspects of sound sources: the number of sound source/s, changing trends in the number of sound source/s (increment/decrement) and category of sound source/s. A laboratory listening test was conducted with 31 participants and data on emotions evoked by the sound source per second, with its different characteristics, were obtained. A linear regression model was established between the three aspects of sound sources mentioned above and emotions. The results reveal the following: first, the number of sound source/s is negatively and positively correlated to the pleasing and arousing dimensions of emotion, respectively; second, changing trends in the number of sound source/s (increment/decrement) has a significant effect on variations in emotions (p < 0.05), but not on emotions itself (p > 0.05); and third, although the category of the sound source/s has a decisive effect on the coordinate range of emotions in a two-dimensional emotion space, the number and changing trends of sound source/s have a limited effect on it. Finally, the linear regression model, composed of the three aspects of sound sources, could explain the values of 33.2% and 28.8% for the pleasantness and arousal dimensions of emotion, respectively.